In a conventional device for utilizing waste heat disclosed, for example, in Japanese Patent Publication No. S63-96449, a component (a condenser) of a refrigerating cycle is commonly used to form a Rankine cycle. The waste heat is collected from an automotive engine (an internal combustion engine) as a driving force by an expansion device, which is also used as a compressor device. The collected driving force is applied (retuned) to the engine.
However, regarding an operation for the Rankine cycle of the device for utilizing the waste heat, it is only disclosed in the publication that a pressure applying pump for the Rankine cycle is activated by switching refrigerant paths after deactivating the refrigerating cycle. Namely, the above publication includes no description for a condition, under which the device for utilizing the waste heat switches between the refrigerating cycle and the Rankine cycle. In addition, the publication has no description how the Rankine cycle is controlled in order to efficiently collect the waste heat. Therefore, it is difficult to put, based on the publication, the device for utilizing the waste heat into a practical use.